We have studied the effect of maternal immunization with type 19F PS-PdB conjugate during gestation and/or lactation on the antibody response and bacterial clearance in the offspring. The conjugate immunogen was injected subcutaneously to mothers during gestation, lactation or both period. Young mice were given an additional dose of conjugate IP during lactation. Serum samples were collected from young mice two weeks after injection. Young mice from mothers that were immunized with the conjugate immunogen and then received an additional dose of conjugate produced significantly higher 19F antibody and anti-pneumolysin levels. The young mice were challenged with 10 to 10 cfu of type 19F cells. At 1, 2, and 4 hrs after bacterial challenge, blood samples were collected and distributed on the sheep blood agar plates. The number of bacterial were significantly lower in experimental groups of young mice from mothers exposed to conjugate immunogen during gestation and lactation than in non- immunized controls. These studies provide further support that maternal immunization with 19F PS conjugated with inactivated pneumolysin has conferred the protective immunity to pneumococcal infection.